Pointing devices, such as mice and trackballs, are well known peripherals for personal computers and workstations. Such pointing devices allow rapid relocation of the cursor on a display screen, and are useful in many text, database and graphical programs. Perhaps the most common form of pointing device is the electronic mouse; the second most common may well be the trackball.
With a mouse, the user controls the cursor by moving the mouse over a reference surface; the cursor moves a direction and distance proportional to the movement of the mouse. Although some electronic mice use reflectance of light over a reference pad, and others use a mechanical approach, most prior art mice use a ball which is on the underside of the mouse and rolls over the reference surface (such as a desktop) when the mouse is moved. In such a prior art device, the ball contacts a pair of shaft encoders and the rotation of the ball rotates the shaft encoders, which historically includes an encoding wheel having a plurality of slits therein. A light source, often an LED, is positioned on one side of the encoding wheel, while a photosensor, such as a phototransistor, is positioned substantially opposite the light source. Rotation of the encoding wheel therebetween causes a series of light pulses to be received by the photosensor, by which the rotational movement of the ball can be converted to a digital representation useable to move the cursor.
Although such a prior art approach has worked well for some time, with high quality mice and trackballs providing years of trouble-free use, the mechanical elements of such pointing devices necessarily limit the useful life of the device.
Optical mice which illuminate a reference pad, while having few or no mechanical parts, have historically been limited due to the need for the reference pad to have a regular pattern, as well as many other limitations.
While optical mice in the prior art have typically required a reference pad, two methods are known in the general optical art for detecting movement of a scattering surface illuminated by coherent illumination. The first such approach employs illumination of the surface with two light sources and using a single detector; the second includes illumination with only a single beam but using a grating filter in front of a single detector. In both these cases, forward and backward movement cannot be distinguished, in what is referred to as sign ambiguity. Likewise, in both case the detection is sensitive to one direction of movement in the plane. Further, in the case of the first prior art approach, the two illuminating beams have to be rotated to be sensitive to another direction of movement; that is, for each direction of movement an independent detection system of illuminating beams and detector has to be used. In the case of the second prior art approach, the grating filter in front of the detector has to be rotated to be sensitive to another direction of movement.
There has therefore been a need for a device which includes a detection system which is sensitive to different directions of movement without alteration of the detection system.